The field of the invention is plasma reactors. Such reactors are commonly used in the desmear/etchback process for printed wiring board fabrication, and they are also used for other etching, cleaning and surface modification uses. One such reactor is shown in U.S. Pat. No. 4,676,865 which utilizes a reactor with heated plates.
The plasma reaction should be controlled so that it provides a uniform action on the entire part being treated.
Prior art designs use either no electrostatic shielding or attempt to strategically locate electrostatic shielding in the zone between the vacuum chamber walls and the plasma electrodes. In the case where no electrostatic shielding is used, major plasma reactions occur between the plasma electrodes and the vacuum chamber walls. This results in plasma etching nonuniformity, and plasma etching speed is severely restricted. When strategically located electrostatic shields are used, only partial improvement results with plasma reaction still occurring in areas not covered by shielding. Additionally, a plasma reaction occurs behind the shielding (that is between the vacuum chamber wall and the shield) because such shielding is not placed in intimate contact with the vacuum chamber walls.